Economists surveyed by WSJ point to low productivity growth and other factors holding down pace of wage gains

U.S. wage growth is set to pick up modestly in the coming years, but economists think pay raises are being depressed by powerful forces—sluggish productivity gains, an aging population and overseas competition—that could persist despite low unemployment.

It is one of the lingering mysteries of the economic expansion that began nearly nine years ago: Why has growth in Americans’ paychecks remained anemic despite the unemployment rate plunging to its lowest level in 17 years?